1. Field of the Invention
The present invention relates to apparatus and a method for evaluating contamination over a substrate surface which is caused by organic substances deposited on thereon, said substrate being used for manufacturing semiconductor devices, liquid crystal displays (LCD), and so forth. More particularly, the invention relates to apparatus and a method for evaluating contamination caused by the organic substances that are contained in the atmosphere of a clean room for manufacturing semiconductor devices, LCDs, and so forth, and are deposited on the surface of the semiconductor substrate, the glass substrate, or the like others.
In the following description, the contamination of this kind is called `atmosphere originated organic contamination` for simplification. Also, in the following description, unless noted otherwise specially, an expression `a substrate` or `the substrate` represents the semiconductor substrate, the glass substrate, or the like others.
2. Description of the Related Art
In the clean room for manufacturing semiconductor devices, LCDs, and other sophisticated products, if organic substances contained in the clean room atmosphere adhere to the insulating film surface that is formed on the semiconductor substrate, the glass substrate, or the like others, they exert a bad influence on the electric characteristics of the semiconductor device and LCD, for instance causing increase of the leakage current and decrease of the breakdown voltage. It might be true that these organic substances deposited on the substrate surface can be readily removed by various rinsing techniques, for instance by the ultraviolet rays/ozone rinsing method. However, since several minutes have to be spent for rinsing one substrate, should it be needed to carry out such rinsing so often, the throughput of the production would be naturally reduced. Therefore, it is desirous to develop a simple method for quantitatively evaluating the atmosphere originated organic contamination. If such a evaluation method is developed and applied to the manufacturing process of semiconductor devices and LCDs, it will become possible to decompose and remove the organic substances deposited on the substrate surface by timely rinsing of the substrate before the atmosphere originated organic contamination reaches such a level that causes deterioration of their electric characteristics. Furthermore, it will become also possible to reduce the number of the steps of rinsing the substrate by carrying out it only when judged necessary in view of the contamination level as evaluated.
It has been known that for evaluating the clean room atmosphere originated organic contamination over the semiconductor substrate and the glass substrate, the quantity of the organic substances deposited on the substrate surface is measured by using the method of X-ray photoelectron spectroscopy (referred to as XPS method hereinafter). In this XPS method, a substrate for use in sampling the contaminants (referred to as the sampling substrate hereinafter) is irradiated with the soft X-rays in the high vacuum circumstances, and the energy and the number of photoelectrons expelled out from said sampling substrate by this X-ray irradiation are measured by the spectrometer, thereby carrying out the qualitative/quantitative analysis of the elements existing on the sampling substrate surface. In the evaluation of the minute atmosphere originated organic contamination quantity over the substrate surface by the XPS method, the evaluation result is expressed as a ratio of the number of carbon atoms to the number of all the atoms existing within the objective region to be analyzed which extends to the depth of several tens angstroms(.ANG.) from the surface, or as a ratio of the number of carbon atoms to the atom number of the known elements existing in said objective region.
Since the atmosphere originated organic contamination quantity can be measured with high precision by the XPS method, this method might be regarded as an effective means for evaluating the atmosphere that causes the atmosphere originated organic contamination over the semiconductor substrate and the glass substrate. However, this method indispensably requires a higher vacuum system and a spectrometer, so that it would highly cost as a whole.
Briefly explaining the analysis by the XPS method, a sampling substrate with a clean surface is first prepared, and then, it is exposed to the objective atmosphere to be evaluated for a predetermined period of time. After this, the sampling substrate has to be transferred to an analyzing room for analysis by an analyzer. Accordingly, in the XPS method, sampling of the contaminants and analysis thereof have to be carried out at separate places. In other words, the analysis by the XPS method can not but be a so-called off-line analysis. Especially, if the XPS apparatus is located at a distance from the sampling point, there can be considered the possibility that the surface of the sampling substrate might be contaminated while it is transferred. Namely, the XPS method must be excellent for the R&D purpose. However, in the actual manufacturing process of semiconductor devices and LCDs, the atmosphere originated organic contamination has to be continuously monitored under the condition that the sampling by the sampling substrate and the analysis thereof can be carried out at an identical place. Therefore, it would be said that the XPS method is not so suitable for the purpose of a so-called in-line analysis.